Print drum mounting means and intermittent drive means therefor

ABSTRACT

A printing drum is connected to a shaft in such a manner as to withstand the severe stresses created in the connection therebetween when the drum is operated in a mode of intermittent rotary motion. A hardened external contacting surface on the shaft is plated with a layer of copper, and a hardened internal contacting surface on the drum is shrink-fitted on said external contacting surface to form said connection.

United States Patent Inventor Melvin A. Soderstrom Dayton, Ohio Appl. No. 763,118

Filed Sept. 27, 1968 Patented Jan. 19, 1971 Assignee The National Cash Register Company Dayton, Ohio I a corporation of Maryland PRINT DRUM MOUNTING MEANs AND INTERMIITENT DRIvE MEANS THEREFOR 1 Claim, 1 Drawing Fig.

U.S. Cl. 101/93, 29/447 Int. Cl B41j 1/34, B41j 23/l4,B23p 11/02 Field oi Search 101/93,

References Cited UNITED STATES PATENTS 6/1914 Davis 29/447 12/1933 Beynon 29/447X 12/1961 Samuels et a1. 29/148.4 7/1966 Doersam 101/93 3/1967 Touchman 101/93 5/1967 Sims 101/93 Primary Examiner-William B. Penn Attorneys-Louis A. Kline, Albert 1.. Sessler, Jr. and Elmer Wargo tion.

BACKGROUND OF THE INVENTlON This invention relates to a rotary drum-type printer which is operated at extremely high stepping rates in an intermittent rotary motion mode, and is particularly concerned with the connection between the printer drum and the shaft on which it is mounted lna conventional drum printer, the type drum rotates at a constant velocity, with printing being done on-the-fly as the type drum rotates. Because the drum on which the type characters are locatedis in continuous rotary motion during printing; any deviation in the time of print hammer impact against said characters results in vertical 'misregistration of the resulting printing.

A printer of the type to which this invention is related is shown inU.S. Pat. No. 3,309,988, which issued Mar. 21, I967, on the application of William S. Touchman and is assigned to the assignee of the present invention. The printer disclosed in U.S. Pat. No. 3,309,988 utilizes a unique method for precision indexing the type drum past the print hammers. The indexing motion of the drum results from rotating a portion of a shaft (on which the drum is mounted) at a constant velocityrotation, and also superimposing a torsional oscillation on another portion of the shaft. The torsional oscillation cycle includes a negative motion component and a positive motion component. When the negative motion component increases to equal the 'magnitude of the forward constant velocity rotation, the effective motion of the drum becomes zero. At this instant, the print hammer strikes the appropriate character on the drum, which is momentarily stationary, to effect the printing free of print smear. After the dwell,'the drum is accelerated in the direction of the forward rotation by the shaft until it reaches a velocity which is substantially twice that of the constantvelocity forward rotation, and then the negative motion increases to complete the cycle. In order to achieve the required angle of oscillation in they shaft (which undergoes torsional strain) while operating with a feasible power level, it is necessary that the drum and shaft system operate at resonance.

indexing a type drum of the variety shown in said patent at speedsof 1,000 to 2,000 steps per second creates a tremendous torque in the shaft and requires that the connection between the type drum and the shaft be capable of transmitting high cyclic loads. The connection must also be able to transmit the torsional angle of oscillation of the shaft to the type drum without loss or slippage. If slippage exists, energy is dissipated, and the system will not oscillate. In addition, slippage generates excessive heat buildup and produces the destructive condition of fretting corrosion at the connection. Fretting corrosion results in surface damage, generally, when there is relative motionbetween solid surfaces in contact under pressure. This corrosion could very well destroy the bond between the type drum and the torsion shaft on which it is mounted and render the system inoperative.

In an effort to overcome the problem of producing a connection between the shaftand the type drum which has the necessary strength and is able to transmit the torsional angle of'oscillation in a printer of the type shown, in said U.S. Pat. No. 3,309,988, various mechanical methods'of joining the type drum and the shaft were investigated. The connection shown in said United States patent is satisfactory from a performance standpoint; however, it is extremely expensive to produce. The connection between the type drum and the shaft shown in the this application performs satisfactorily and is very economical to produce.

SUMMARY OF THE INVENTION This invention relates to the connection between a shaft and LII contacting surface thereon, and the type drum has a hardened internal contacting surface therein. The shaft diameter and the internal diameter of the type drum at said contacting surface are so dimensioned as to provide an interference fit therebetween prior to assembly. A layer of metal like copper, which'is softer than said contacting surfaces, is deposited on the shaft at its contacting surface, after which the type drum is shrink-fitted on to the shaft so as to provide a shrink-fit connection between said hardened surfaces. Such a connection provides an unexpectedly'strong joint which is capable of transmitting the torsional oscillations of the shaft and is economical to produce.

DESCRIPTION OF THE DRAWING FIG. 1 is a general perspective view, partly in cross section, of this invention, showing the connection between the shaft and the type drum for a printer system which operates on the principles disclosed in said U.S. Pat. No. 3,309,988.

DESCRIPTION'OF THE PREFERRED EMBODIMENT FIG. I is a general perspective view of a portion of a printer system in which the connection of this invention may be used. The printer system includes supports 10 and 12, in which bearings 14 are located to rotatably support a shaft 16. The shaft 16 has an enlarged diameter portion 18 in the center thereof, and two driving surfaces 20. (only one shown), located equidistantly from said portion 18. Each driving surface 20 has its own driving pulley 22 operatively connected thereto, and each pulley 22 is driven in timed relation with the other at a constant rotary velocity by its own driving belt 24. A cylindrical type drum 25, having printing characters (not shown) thereon, is secured to the portion 18 of the shaft 16 by a connection to be described later. As the pulleys 22 are rotated, the shaft 16 and the drum 25 are rotated clockwise, as viewed in FIG. 1.

A torsional oscillation is imposed on the shaft 16 in P16. 1 by the following construction. Near each end of the shaft 16, there is positioned an oscillator or exciter 26. Each oscillator 26, which may be magnetically operated, includes a rotor member 28, which is fixed to the shaft '16 to rotate therewith, and a stator member 30 secured to the respective adjacent supports 10 and 12. The rotor and stator members of each a type drum in a printer operating under the principles dis- I making saidconnection. The shaft has a hardened external oscillator 26 are in flux coupling relationship with each other, and each oscillator 26 is equidistantly located from its associated driving surface 20. As the shaft 16 and the drum 25 are rotated clockwise (as viewed in FIG. 1) by the pulleys 22, and as they approach operating speed of about 950 to 1,900 r.p.m., the oscillators 26 are energized. Upon energization, each oscillator 26 works to excite its associated end of the shaft 16 counterclockwise, so as to superimpose a torsional oscillation on the forward constant velocity rotation imparted by the pulleys 22. The torsional oscillation has a cycle which includes a negative motion component and a positive motion component. When the negative motion component increases to equal the magnitude of the forward constant velocity, the effective motion of the drum becomes zero, or it dwells, during which time printing may be effected. After the dwell, the drum oscillates in the direction of the forward rotation of the shaft (positive motion component) until it reaches a velocity which is substantially twice that of the constant velocity forward rotation. The negative motion component then follows. In order to achieve the required angle of oscillation in the shaft 16 (which undergoes torsional strain) while operating with a feasible power level, it is necessary that the drum 25 and the shaft 16 operate at resonance as disclosed in said patent.

The oscillators 26 (FIG. I) excite the shaft 16 so as to cause it to oscillate at rates of 1,000 to 2,000 cycles per second, so as to provide as many indexes of the drum 25 per second. It is apparent that, with such high stepping rates, the connection between the drum 25 and the shaft 16 is subjected to extreme stress concentration.

The shaft 16, the type drum 25 (FIG. 1 and the connection therebetween are constructed as follows. The shaft 16 in the embodiment shown is rough machined to the shape shown from AlSl 52100 vacuum melt steel. After a conventional, heat-treating, stress-relieving operation, the shaft l6is finish machined. The shaft 16 is then packed in charcoal to keep the surface of the shaft from decarburizing during a following heat-treating operation. A holder (not shown) is welded to one end of the shaft 16 to provide a means for suspending the shaft from that end during the heat-treating operation. The shaft 16, while suspended from said holder, is given a conventional heat treatment to produce an austenitic structure for the specified steel. After this heat treatment, the shaft 16, while suspended from said holder, is quenched in an oil bath. After quenching, the shaft 16 is examined for eccentricity or runout. The shaft 16 is then placed in a tempering furnace in a horizontal position, so as to place any high side which appears on the shaft in the up position, and a load (up to 500 pounds) is placed on the high side during this tempering operation (to reduce runout without inducing internal stresses), which takes place in a forced-air furnace at 450 F. for a period of 2 hours. After this tempering operation, the shaft 16 is conventionally stabilized by freezing the shaft at minus 120 F. for a period of 2 hours. The shaft 16 is then put into a forced-air tempering furnace at 450 F. for a period of 2 hours, during which time no load is permitted on the shaft. The portion 18 of the shaft 16 should now record a Rockwell hardness reading of 58 to 60.

After the shaft 16 has been formed and heat treated as previously explained, the holder is removed, and the entire surface of the shaft is ground in a grinding operation, and elliptical fillets 40 are ground on both sides of the portion 18, as shown, with the longer radius of the ellipse being tangent to the length of the shaft 16. These elliptical fillets 40 minimize stress concentration better than strictly radial fillets do. Following the grinding operation. a layer of copper of about 0.005 inch (not shown) is deposited on the portion 18 of the shaft by a conventional plating operation. After the copper layer is deposited. the portion 18 is finish-ground to leave about 0.0005 inch of copper on the portion 18.

In constructing the drum 25, the rotational inertia is of pri mary significance in establishing the geometry of the torsional system shown in FIG. 1. Because the length of the drum 25 is established by the printing column capacity of the system shown, and the diameter of the drum is established to a great extent by the size of characters selected to be formed on the drum, the primary effort to reduce rotational inertia was directed towards its weight distribution. After experimentation with various metals, the drum 25 was made of A-l tool steel with a wall thickness of about 0.125 inch except for the center portion 32 at the center thereof. This center portion 32 was made to a thickness of about 0.50 inch and is stepped as at 34 between the internal diameter 36 of the center portion 32 and the thin wall 38 to provide for a preferential distribution of the load at the connection between the shaft 16 and the drum 25. The drum 25 is then heat treated by conventional techniques to harden it.

After the drum 25 is constructed, as stated above, the internal diameter 36 thereof at the center portion 32 is finish ground to have it about 0.004 inch smaller than the external diameter of the portion 18 of the shaft 16 with the layer of copper thereon. The type characters (not shown) are then formed on the periphery of the drum 25 by conventional machining techniques. After the characters are formed on the drum 25, the drum is heated to about 450 F. and the shaft is frozen at about minus l F. to enable the drum to be slipped over the shaft to effect a shrink-fit connection between the portion 18 on the shaft 16 and the center portion 32 of the drum 25. After the drum is positioned on the shaft 16, the assembly is allowed to reach equilibrium at room temperature to effect said shrink-fit connection.

It is not understood why a shrink-fit connection between the upon it; however, it performs much better than two hardened I surfaces which are conventionally shrink-fitted together. A

hardened drum 25 was necessary for producing satisfactory printed characters, and a hardened shaft was necessary for handling the cyclic loads involved. These two requirements negated the use of a conventional shrink-fit connection.

After the drum 25 is connected to the shaft portion 18, a group of sound-damping rings 42 are secured to the inner wall of the drum 25 as shown. These rings 42 are made of phenolic material and have grooves on their outside wall to receive an adhesive, like epoxy, which is used to cement the rings in spaced relation along the interior of the drum 25. The rings 42 are spaced to prevent contact with one another to avoid the generation of noise.

The pulleys 22 are shrink-fitted on their respective driving surfaces 20 by conventional techniques. These driving surfaces 20 are located at nodal points along the shaft 16. After the pulleys 22 are secured to the shaft 16, the rotors 28, which are made of soft steel, are conventionally shrink-fitted on their respective ends of the shaft 16, and the ends of the shaft 16 are mounted in their respective bearings 14.

lclaim:

l. in a printing system comprising:

a torsion shaft;

a printing drum attached to said shaft at a medial portion thereof;

means for continuously rotating said shaft at a substantially constant speed in one direction during successive printing cycles past a print point;

oscillator means connected to said shaft ends for oscillating said shaft to cause said drum to effectively dwell one or more times for each revolution of said drum;

said shaft having a hardened external contacting surface at said medial portion with a layer of copper approximately 0.0005 inch thick adhering to said external surface;

said drum having a hardened internal contacting surface;

the external contacting surface of said shaft with the layer of copper thereon and the internal contacting surface of said drum being dimensioned to provide an interference fit therebetween when the drum is assembled on said shaft; and

said drum being shrink-fitted on said shaft. 

1. In a printing system comprising: a torsion shaft; a printing drum attached to said shaft at a medial portion thereof; means for continuously rotating said shaft at a substantially constant speed in one direction during successive printing cycles past a print point; oscillator means connected to said shaft ends for oscillating said shaft to cause said drum to effectively dwell one or more times for each revolution of said drum; said shaft having a hardened external contacting surface at said medial portion with a layer of copper approximately 0.0005 inch thick adhering to said external surface; said drum having a hardened internal contacting surface; the external contacting surface of said shaft with the layer of copper thereon and the internal contacting surface of said drum being dimensioned to provide an interference fit therebetween when the drum is assembled on Said shaft; and said drum being shrink-fitted on said shaft. 